1. Field of the Invention
The present invention relates to protocols used for managing compression resources distributed in a network, and more particularly to techniques for avoiding the use of compression resources on data that has already been compressed, or is otherwise less suitable for compression by intermediate links in a network.
2. Description of Related Art
The Internet includes a web of communication links through which data paths are established from end station to end station. End stations setup sessions using protocols such as the Transmission Control Protocol over the Internet Protocol TCP/IP or the User Datagram Protocol over the Internet Protocol UDP/IP. Packets in the sessions are routed through the links in the web and traverse intermediate stations.
Links between intermediate stations in the web are managed independent of, and often transparent to, the end stations. For example, intermediate stations interconnected by a long distance link may perform functions such as encryption, tunneling, and compression. One intermediate station function involves standard IPSEC Internet protocol security specified in RFC 1826 and RFC 1827. IPSEC is established between intermediate stations, for example between routers at separate campuses of a company. In this way, data sent between the campuses is protected. It is desirable to compress the data being sent between the campuses in order to preserve bandwidth. Also it is found that data which has been encrypted does not compress well because the encryption protocol tends to randomize the data and make it more difficult to compress. Thus, installations which apply the IPSEC protocol across intermediate links compress the data prior to encryption. The compressed data is encrypted and transmitted across the links to the remote campus.
However, not all data is suitable for compression. Thus, the compression resources at these intermediate stations are being wasted on certain kinds of data. For example, end stations may send data which has already been compressed between one another. To compress it once again at an intermediate station will not yield significant difference in its size.
Accordingly, it is desirable to provide a technique by which the resources at intermediate stations in the network can be conserved while maintaining the efficient use of the available bandwidth.